1. ‘Reason is and ought only to be the slave of the passions, and can pretend to no other office, but to serve and obey them.’ (Hume, Treatise of Human Nature (THN) 2.3.3) Unfortunately, Hume uses ‘reason’ to mean ‘discovery of truth or falsehood‘ (THN 3.1.1) as well as discovery of logical relations. So suppose we avoid, as Hume I think does not, prejudging the question of how many ingredients are requisite for action, by separating these two claims out:
A. Reason (= logical powers) is and ought only to be the slave of the passions.
B. Reason (= belief(s)) is and ought only to be the slave of the passions.